Display screen using variable resistance memory semiconductor

ABSTRACT

An electrically operated display screen including a support surface on which active layers, preferably of electroluminescent phosphor having a nonlinear voltage-brightness characteristic and variable resistance memory semiconductor materials, are deposited one adjacent the other with transparent conductive layers disposed on either side thereof to provide electrode surfaces for connection to an alternating current voltage source which substantially excites the electroluminescent layer to generate relatively high-intensity visible light in those areas thereof where the variable resistance memory semiconductor material is in the low-resistance condition. The layer of memory semiconductor material has discrete portions which are individually alterable between stable high- and low-resistance conditions by application of predetermined amounts of energy to form the desired visible light patterns on the display screen.

United States Patent Ovshinsky 1 Feb. 22, 1972 [54] DISPLAY SCREEN USING VARIABLE RESISTANCE MEMORY SEMICONDUCTOR [72] Inventor: Stanford R. Ovshlnsky, Bloomfield Hills,

Mich.

[73] Assignee: Energy Conversion Devices, Inc., Troy,

Mich.

[221 Filed: May 16, 1969 [21] Appl.No.: 825,289

[52} US. Cl. ..250/213 R, 313/108 A, 340/173 SS [51] ..1101l17/00 [58] Field of Search ..250/213, 83.3 1R; 340/173 LS; 313/108 A [56] References Cited UNITED STATES PATENTS 2,989,641 6/1961 Nicol] ..250/213 3,271,591 9/1966 Ovshinsky. ....340/l73 X 3,286,027 11/1966 Martel ..250/213 X 3 ABSTRACT An electrically operated display screen including a support surface on which active layers, preferably of electroluminescent phosphor having a nonlinear voltage-brightness characteristic and variable resistance memory semiconductor materials, are deposited one adjacent the other with transparent conductive layers disposed on either side thereof to provide electrode surfaces for connection to an alternating current voltage source which substantially excites the electroluminescent layer to generate relatively high-intensity visible light in those areas thereof where the variable resistance memory semiconductor material is in the low-resistance condition. The layer of memory semiconductor material has discrete portions which are individually alterable between stable highand low-resistance conditions by application of predetermined amounts of energy to form the desired visible light patterns on the display screen.

18 Claims, 7 Drawing Figures DISPLAY SCREEN USING VARIABLE RESISTANCE MEMORY SEMICONDUCTOR This invention relates generally to display screens, and more particularly to electrically operated luminescent display screens for displaying a picture of information to a viewer.

An object of this invention is to provide a luminescent display screen which, at any given time, has a fixed pattern of light-emitting portions forming a given display pattern and wherein the display pattern can be readily altered.

The luminescent display screen of this invention may be flat or arcuately shaped viewedin cross section and have any desired length and width. The screen is a relatively thin laminate body of adjacent layers of conductive, variable resistance memory semiconductor, and luminescent-materials. The luminescent layer is most desirably an electroluminescent material having a nonlinear voltage-brightness characteristic such that there is provided a region where small changes of AC voltage applied thereto will cause relatively large changes in brightness of visible light output. A light transparent conductive electrode-forming layer, such as tin oxide (SnO is formed on the outer side of the layer of luminescent material. The luminescent layer is most desirably a continuous layer of luminescent material, but it can be divided into separated, closely spaced areas or spots of such luminescent material. There is provided immediately behind the luminescent layer a layer of variable resistance memory semiconductor material also most advantageously formed as a continuous layer of such material. A layer of light transparent conductive electrodeforming material, which also may be of tin oxide, is placed on the outside of the memory material. The layer of variable resistance memory semiconductor material is such that discrete portions thereof can be readily alterable between stable highand low-resistance conditions by application of suitable amounts of energy through the light transparent layer in contact therewith, such energy may be in the form of a laser beam and/or a photoflash lamp. These discrete portions of the layer of variable resistance memory semiconductor material act as switches between the last-mentioned conductive layer and the luminescent layer. A source of voltage, preferably an alternating current voltage source where an electroluminescent material is used, is applied across the light transparent electrode-forming conductive layers so that increased voltage is applied only to the discrete portion of the layer ofluminescent material opposite discrete portions of the layer of variable resistance memory semiconductor material that are in the lowresistance condition, so that a light pattern is emitted by the layer of luminescent material which corresponds to the pattern of highand low-resistance portions of the layer of variable resistance memory semiconductor material. The amplitude and/or frequency of the output of said source of voltage must be sufficiently low as not to affect the highor lowresistance condition of the layer of variable resistance memory semiconductor material. The layers of the display screen between the luminescent material and what is to be the front visible side ofthe screen must be transparent to the light emitted in the latter layer. The display pattern can be formed on the display screen by selectively impinging a modulated beam of energy, such as, a laser beam, on the memory semiconductor layer for changing desired discrete portions thereof from a high-resistance condition to a low-resistance condition, and the display pattern may be erased by applying energy, such as, for example, energy from an electron beam, laser beam, spark discharge or high-intensity photoflash lamp light, to the memory semiconductor layer. The display pattern formed on the display screen can be changed to a new display pattern by modifying the existing pattern of highand low-resistance portions on the variable resistance memory semiconductor layer by a modulated beam of energy, such as a laser beam, modulated in accordance with the new display pattern. It is most advantageous to provide a display screen with the energy generating means mounted behind the screen, with the memory semiconductor layer thereof rearwardly of the luminescent layer. In such case, the electrode-forming layer on the rear side of the memory semiconductor layer is transparent to said energy and the electrode-forming conductive layer on the front side of the luminescent layer is transparent to the light emitted by the luminescent layer.

The memory semiconductor material, which is capable of having desired discrete portions thereof reversibly altered or changed between a stable high-resistance condition and a stable low-resistance condition, is preferably a polymeric material which, in a stable manner, may be normally in either of these conditions and a large number of different compositions may be utilized. As for example, the memory semiconductor material may comprise tellurium and germanium at about percent tellurium and 15 percent germanium in atomic percent with inclusions of some oxygen and/or sulphur. Another composition maycomprise Ge As Se Still other compositions may comprise Ge Te, S and P or Sb and Se Se, S and P or Sb Further compositions which are also effective in accordance with this invention may consist of the memory materials disclosed in Stanford R. Ovshinskys US Pat. No. 3,271,591, granted on Sept. 6, 1966, (such materials being sometimes referred to therein as Hi-Lo and circuit breaker device materials). By appropriate reduction of compositions and thicknesses of layers, desired resistances and capacitances in the lowand high-resistance conditions may be obtained.

Assuming the layer of memory semiconductor material to be in its stable high-resistance condition, desired discrete portions thereof may be altered to a stable low-resistance condition by energy applied thereto which can be in the form of energy pulses of sufficient duration (e.g., 1-100 milliseconds or more) to cause the alteration to the low-resistance condi tion to take place and be frozen in. Such desired discrete portions may be realtered to the stable high-resistance condition by energy applied thereto which can be in the form of energy pulses of short duration (e.g., 10 microseconds or less) to cause the realteration to the high-resistance condition to take place and be frozen in.

Conversely, assuming the layer of memory semiconductor material to be in its stable low-resistance condition, desired discrete portions thereof may be altered to a stable high-resistance condition by energy applied thereto which can be in the form of energy pulses of short duration (e.g., l0 microseconds or less) to cause the alteration to the high-resistance condition to take place and be frozen in. Such desired discrete portions may be realtered to the stable low-resistance condition by energy applied thereto which can be in the form of energy pulses of sufficient duration (e.g., 1-100 milliseconds or more) to cause the realteration to the low resistance condition to take place and be frozen in.

The reversible alteration of desired discrete portions of the layer of the memory semiconductor material between the high resistance or insulating condition and the low resistance or conducting condition can involve configurational and conformational changes in atomic structure of the semiconductor material which is preferably a polymeric-type structure. These structural changes, which can be of a subtle nature, may be readily effected by applications of various forms of energy at the desired discrete portions of the layer. It has been found, particularly where changes in atomic structure are involved, that the high-resistance and low-resistance conditions are substantially permanent and remain until reversibly changed to the other condition by the appropriate application of energy to make such change.

In its stable high resistance or insulating condition, the memory semiconductor material (which is preferably a polymeric material) is a substantially disordered and generally amorphous structure having local order and/or localized bonding of the atoms. Changes in the local order and/or localized bonding which constitute changes in atomic structure, i.e., structural changes, which can be of a subtle nature, provide drastic changes in the electrical characteristics of the semiconductor material, as for example, resistance, capacitance, dielectric constant, and the like. These changes in these various characteristics may be used in determining the structure of the desired discrete portions with respect to that of the remaining portions of the layer of semiconductor material.

The changes in local order and/or localized bonding, providing the structural change in the semiconductor material, can be from a disordered condition to a more ordered condition, such as, for example, toward a more ordered crystallinelike condition. The changes can be substantially within a short range order itself still involving a substantially disordered and generally amorphous condition, or can be from a short-range order to a long-range order which could provide a crystallinelike or pseudocrystalline condition, all of these structural changes involving at'least a change in local order and/or localized bonding and being reversible as desired. Desired amounts of such changes can be effected by applications of selected levels of energy.

The aforementioned alterations can be effected in various ways, as by energy in the form of electric fields, radiation of heat, or combinations thereof, the simplest being the use of heat. For example, where energy in the form of electromagnetic energy, such as, laser beams, photoflash lamp light, or the like, is used both radiation and heat can be involved. Where energy in the form of particle beam energy, such as electron or proton beams, is used, in addition to heat, there also can be involved a charging and flooding of the semiconductor material with current carriers. Since heat energy is the simplest to use and explain, this invention will be considered by way of explanation in connection with the use of such heat energy, it being understood that other forms of energy may be used in lieu thereof or in combination therewith within the scope ofthis invention.

When energy in the form of energy pulses of relatively long duration is applied to desired discrete portions of a layer of memory semiconductor material in its stable high resistance or insulating condition, such portions are heated over a prolonged period and changes in the local order and/or localized bonding occur during this period to alter the desired discrete portions of the semiconductor material to the stable low-resistance condition which is frozen in. Such changes in the local order and/or localized bonding to form the stable low-resistance condition can provide a more ordered condition, such as, for example, a condition toward a more ordered crystallinelike condition, which produces low resistance, as mentioned hereinabove.

When realtering the desired discrete portions of the memory semiconductor material from the low-resistance condition to the high-resistance condition by energy in the form of energy pulses of relatively short duration, sufficient energy is provided to heat the desired discrete portions of the semiconductor material sufficiently to realter the local order and/or localized bonding of the semiconductor material back to a less-ordered condition, such as back to its substantially disordered and generally amorphous condition of high resistance which is frozen in. These same explanations apply where the normal condition of the memory semiconductor material is the low resistance or conducting condition and where the desired discrete portions thereof are altered to the high resist'ance or insulating condition. In the memory semiconductor materials used in this invention, it is found that the changes in local order and/or localized bonding as discussed above, in addition to providing changes in electrical resistance, they also provide changes in capacitance, dielectric constant and the like.

The energy applied to the memory semiconductor material for altering and realtering the desired discrete portions thereof may take various forms, as for example, electrical energy in the form of voltage and current, beam energy, such as electromagnetic energy in the form of radiated heat, photoflash lamp light, laser beam energy or the like, particle beam energy, such as electron or proton beam energy, energy from a high-voltage spark discharge or the like, or energy from a heated wire or a hot airstream or the like. These various forms of energy may be readily modulated to produce narrow discrete energy pulsations of desired duration and of desired intensity to effect the desired alteration and realteration of the desired discrete portions of the memory semiconductor material, they producing desired amounts oflocalized heat for desired durations for providing the desired pattern of information in the layer of the memory semiconductor material.

The pattern of information so produced in the layer of memory semiconductor material described remains permanently until positively erased, so that it is at all times available for display purposes. Also, by varying the energy content of the various aforesaid forms of energy used to set and reset desired discrete areas of the memory semiconductor material, the magnitude of the resistance and the other properties referred to can be accordingly varied with some memory materials.

Therefore, when the memory semiconductor material described above is used to form a part of a display screen as contemplated by this invention many advantages are obtained. For example, a particular display pattern is quickly and easily modified or completely eliminated and a new display pattern put in its place on the same screen. Also, different light intensities may be obtained at different discrete points of the screen which may vary between complete absence or substantially complete absence of emitted light and the maximum amount of emitted light possible to achieve with the particular luminescent material being used. This variation oflight intensity is made possible by the different relative states of conductivity of the memory semiconductor material used or by controlling the number of dots or discrete points which are permitted to be conductive. Also, when using luminescent materials such as AC-operated electroluminescent materials, desirable amounts of light variation between the minimum and maximum values is most advantageously obtained by selecting such materials having a nonlinear voltage-brightness characteristic. Such electroluminescent materials are well known, and, in addition, there is known several methods of making electroluminescent material nonlinear or more nonlinear.

The display screen of this invention may take various forms, as for example, the screen may be an integral part of the scanning and resetting apparatus located behind the screen with the screen forming one wall of an enclosure. Another form would include only the screen which had a display pattern formed thereon so that when operating voltage is applied to the electrode layers, the pattern will appear as distinctive light emitting portions, the display screen of the latter form being relatively thin and capable of wall mounting similar to that ofa picture.

Many objects, features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

FIG. 1 is a diagrammatic enlarged view ofthe display screen of the invention in fragmentary section and the associated means for operating the same;

FIG. 2 is a perspective view of the entire display screen device of FIG. 1 illustrating one form of the invention;

FIG. 3 is a front view of the display screen without the scanning apparatus and illustrates another form of the invention;

FIG. 4 is an equivalent electric circuit of a discrete portion of the display screen when the variable resistance memory semiconductor material thereof is in its high-resistance condition;

FIG. 5 is an equivalent electric circuit of a discrete portion of the display screen when the variable resistance memory semiconductor material is in a low-resistance condition;

FIG. 6 shows the current-voltage characteristics of the various component layers of the display screen under the various conditions of operation thereof; and

FIG. 7 shows a voltage-brightness characteristic of a suitable AC-operated electroluminescent material which can be used with this invention.

Referring now to FIG. lthere is shown a rectangular display screen designated generally by reference numeral 9 illustrated as being of a flat or straight configuration, viewed in cross section, it being understood that the screen may be curved viewed in cross section and have other than a rectangular shape. In the most advantageous form of this invention the screen is a laminate body comprising various layers deposited on a substrate or support base 11 which is preferably made of material transparent to energy beams 10 and 10a shown here as one method used to set and reset a display pattern on the display screen 9. In the example of the invention being described the energy beams 10 and 10a are laser and photoflash lamp beams respectively and so the substrate 11 is made of relatively thin visible light transparent glass or plastic material. A thin layer 12 of conductive material, also transparent to visible light, such as, tin oxide (SnO is deposited on the substrate 11 to form an electrode for connection to a source of voltage.

Deposited over the transparent conductive layer 12 is a layer 13 of variable resistance memory semiconductor material of the type described hereinabove which is capable of having discrete portions of the material being reversibly altered by the beams 10 and 10a between a high-resistance blocking condition and a low-resistance conducting condition. Deposited over the variable resistance memory layer 13 is a layer 14 of electroluminescentmaterial,such as, zinc sulphide (ZnS which emits light from selected portions of the material as a result of alternating current voltage applied to these selected portions, and overlying the layer 14 of electroluminescent material is a layer 16 of transparent conductive material, such as, tin oxide (SnO which serves as the other sheetlike electrode layer for the display screen. If desired, a layer 15 of transparent insulating material, such as, glass or the like, may be positioned over the layer 16 to insulate the outer surface of the display screen 9. Operating voltage is applied to the display screen 9 by electrical connection ofa volt age source, such as, an AC-voltage source, to the layers 12 and 16 to cause small amounts of current to flow between these layers in the regions of low resistance of the layer 13 to energize the adjacent areas of the luminescent material of layer 14. Extremely small amounts of leakage current may flow between the electrode layers 12 and 16 in the regions of the memory semiconductor material in the high-resistance condition, but, due to the proper selection of luminescent material having a nonlinear voltage-brightness characteristic the small amounts of leakage current will have little or no noticable affect on the light output in these regions.

The layers 12, 13, 14, 15 and 16 may be deposited films which can be deposited by vacuum deposition of by sputtering or the like. After the layer 13 of variable resistance memory material is applied to the screen 9, as well as the other layers 12, 14 and 16, the display screen is positioned in proximity to an energy source 17 which may be located within a closure 18, seen in FIG. 2, the screen being the front wall thereof, and the energy beam 10 is directed toward the display screen to penetrate the support base 11 and electrode layer 12 to impinge upon the surface of the layer 13 to alter selected portions of the layer from its stable high-resistance condition to its stable low-resistance condition. The energy source 17 may be a laser diode which directs a very small beam upon the memory layer 13. The beam 10 is deflected by a deflection device 20 to effect movement of the beam through the desired predetermined pattern corresponding to the pattern to be displayed from the surface of the display screen 10. impingement of the energy beam 10 on the variable resistance memory material of layer 13 will cause the material to alter from its substantially high-resistance blocking condition to its low-resistance conducting condition only in the regions receiving the beam energy. Therefore, as the energy beam 10 is deflected from side to side or through a desired pattern by the influence of the deflection device 20, discrete elemental lengths ofthe variable resistance memory material 13 will form conductive paths through the material. These discrete conductive paths will 7 allow an increased voltage to be applied to the immediately adjacent portions of the layer 14 of luminescent material and this increased voltage will cause a corresponding increase in current to energize the material to emit light therefrom at these regions while other portions of the material will emit little or no light.

The preferred form of beam energy is that of modulated beam pulses, as indicated by the square wave pulses 21 and 22, it being understood that other forms of beam energy may be used. When the layer 13 of memory-type material is deposited, the entire surface area and thickness of the layer is in a substantially disordered generally amorphous condition of high resistance. To selectively alter desired portions of the semiconductor material from this high-resistance blocking condition to a low-resistance conducting condition, the beam 10 is modulated to form beam pulses of relatively long duration, as indicated by pulses 21 to change the local order and/or localized bonding of the molecular structure of the memory material to create the desired discrete low-resistance conductive paths through the material. On the other hand, if it is desired to realter the memory material from its low-resistance conducting condition to the original high-resistance blocking condition only at selected regions thereof, the beam energy 10 is modulated with short duration beam pulses, as indicated by the pulses 22, which tend to rearrange or reform the local order and/or localized bonding of the molecular structure to substantially its original condition of high resistance. When the beam 10 is modulated by pulses 21, the pulses of beam energy are applied for a sufficient period of time to allow the change of conductivity to take place, for example, a millisecond or so and the movement of the energy beam is sufficiently slow to ensure overlap of beam pulses applied to the surface of the semiconductor material thereby ensuring a continuous conductive path through the thickness of the material as well as along the desired length of the material;

On the other hand, if the entire area of the memory material oflayer 13 is to be realtered to its original condition of high resistance, this may be accomplished by a single flash of light from a high-intensity photoflash lamp 23 (a Xenon photoflash lamp being a particularly useful and effective photoflash lamp) which directs the wide angle light beam 10a to impinge upon the entire area of the layer 13, and thereafter a completely new display pattern can be formed on the screen 9. A suitable control means 24 is provided to control the energy source 17, deflection device 20 and the photoflash lamp 23. The control means 24 may be in a console attached to or separate from an enclosure 18. Operating voltage is applied to the control means 24 and screen 9 by one or more cables 25. However, the flat display screen can be a separate wall mounted unit 9a as shown in FIG. 3 where it has its display pattern modified or changed at a location remote from its normal location. Also, the screen 9 in FIG. 2 may be made removable from the enclosure 18 so it can be replaced by another screen like 92 which can be remotely set to a desired display pattern. The control means 24 may include a scanning photodensitometer, a device well known in the art, which scans printed matter and develops pulses responding to the light or dark areas of the information being scanned. The scan control of the photodensitometer may be operated in synchronism with the control means 17 and the deflection device 20.

A source 28, preferably of alternating current voltage where AC-operated electroluminescent materials are used, is connected to the electrode layers 12 and 16, so energizing current will flow between the electrode layers through the low-resistance portions 26, 27, etc., (FIG. 1) of the memory layer 13 and the immediately adjacent portions 26a and 27a of the electroluminescent layer 14. The voltage amplitude of the voltage source 28 is preferably maintained at all times below the threshold voltage value of the memory material such that the applied voltage will not cause changes in the resistance condition of the memory material. The portions of the luminescent layer 14 through which the voltage is sufficiently increased become energized to emit light thereby forming the desired display pattern on the display screen 9.

The variable resistance memory semiconductor material of the layer 13 is symmetrical in electrical operation in that it conducts current substantially equally in both directions in its low-resistance condition, and blocks current substantially equally in both directions in its high-resistance condition. Therefore, when voltage is applied to electrodes 12 and 16, the entire screen surface appears electrically to be a plurality of parallel connected circuits with the majority of the current flow passing through the low-resistance parallel circuits and each of these parallel circuits providing a different voltage to be applied at different selected areas of the luminescent layer 14, more voltage causing substantial light to be emitted and less voltage causing little or no light emission.

Although the broad aspects of this invention can be utilized with luminescent materials or devices of various kinds it is herein disclosed in conjunction with AC-operated electroluminescent materials the use of which provides several advantages in constructing display screens in accordance with this invention. Such advantages are ease of manufacture, lowcost, low-power consumption and reliability. Electroluminescent phosphor materials can be deposited on large areas such as by vapor deposition, painting or other equally simple methods. Also, electroluminescent phosphor materials have, for the most part, very high dielectric constants thereby being substantially voltage responsive rather than current responsive, there being small amounts of current passing through such materials while in the energized light-emitting state. Typical orders of magnitude of dielectric constant of electroluminescent phosphor materials are l"l0 ohms/cm. although other orders of magnitude may be obtained. However, when using electroluminescent phosphor materials of this type in conjunction with the memory semiconductor material disclosed herein it becomes necessary, for best results, to use such phosphor materials having a nonlinear voltagebrightness characteristic. This is because of the dielectric constant of the memory semiconductor material is many orders of magnitude less than the dielectric constant of the phosphor material. As for example, the dielectric constant of present memory semiconductor materials may be between lO -lO ohms/cm. Therefore, with the deposited layer construction of a display screen as disclosed herein, a majority of the applied voltage will be impressed across the electroluminescent material even with the memory semiconductor material in its high-resistance blocking condition. To compensate for the disparity of the dielectric constants between the two active materials it is contemplated in accordance with one aspect of this invention to use in combination with such memory semiconductor materials an electroluminescent material having a nonlinear voltage-brightness characteristic similar to that shown in FIG. 7. Here, changes of voltage applied across the electroluminescent material cause changes of brightness as indicated by the nonlinear curve 29, there being a region 29:: where relatively small changes of voltage cause relatively large changes of brightness. By way of example, a point 29b on the curve 29 indicates the amount of brightness obtained with approximately 80 volts applied across the electroluminescent material while a point 29c indicates the amount of brightness with approximately 120 volts applied across the electroluminescent material, there being a substantial spread between these two brightness conditions to provide the necessary contrast for a display panel. Therefore, and by way of example, when 120 volts AC is applied the electrode layers 12 and 14 by the voltage source 28, with the memory semiconductor material in its high-resistance blocking condition, and with layers of memory and electroluminescent materials of approximately equal thickness, approximately 80 volts will be impressed across the electroluminescent layer thus providing little or no light output and 40 volts will be impressed across the memory semiconductor material, this 40- volt value being less than the voltage threshold level of the memory semiconductor material. However, when the desired discrete portions 26 and 27 of the layer 13 of memory semiconductor material are altered from the high-resistance blocking conditions to the low-resistance conducting condition substantially the entire value of the applied voltage, i.e., volts, will be impressed across the electroluminescent material 26a and 27a adjacent the portions 26 and 27, and relatively large amounts oflight will be emitted therefrom,

For a better understanding of the electrical properties of the display screen of this invention, reference is now made to H6. 4 which illustrates the equivalent electric circuit of a portion of the display screen which has the memory semiconductor material in a high-resistance blocking condition. A capacitor 30 is shown representing the capacitive reactance ofa discrete portion of the memory material in its high-resistance condition and resistor 31 represents the high-leakage resistance thereof. A capacitor 32 is shown representing the capacitive reactance of the discrete portion of the electroluminescent layer 14 in front of the discrete portion of the memory semiconductor material represented by capacitor 30 and resistor 31. The relative capacitances of the layer 13 of memory semiconductor material and the electroluminescent layer 14 are a function of the relative thicknesses and dielectric constants of the materials involved and are selected so enough capacitive reactance is in series with the electroluminescent material to reduce the voltage thereon to a value where little or no light output is obtained when the memory semiconductor material is in the high-resistance condition. Therefore, application of alternating current voltage across discrete portions of the layers of memory and electroluminescent materials represented by the capacitors 30 and 32, respectively, will result in sufficient voltage being dropped across the memory material with the remainder of the voltage dropped across the electroluminescent material, so little or no light will be emitted by the electroluminescent material involved. The reactive impedance characteristics of the serially connected components is shown in the HO. 6 which illustrates the capacitive reactive impedance of capacitor 32 by the slope of curve 34, and the capacitive reactance of the capacitor 30 by the slope of curve 35.

However, when a discrete portion of the memory material is altered from its highqesistance blocking condition to its lowresistance conducting condition, it acts as a low-value resistor represented by the resistor 36 of FIG. 5 which has a resistance significantly low in value, so substantially all of the voltage from the source 28 is applied across the capacitor 32. The resistance or impedance characteristic of the semiconductor material represented by the resistor 36 is illustrated by the curve 37 of FIG. 6.

Accordingly, this invention provides a display screen of unitary construction wherein selected portions of the screen are energized to display light therefrom while unselected portions remain deenergized, and wherein the display pattern formed on the screen can be easily altered or modified by resetting the low-resistance conductive condition of the semiconductor material to its original high-resistance blocking condition and then selectively setting another pattern of low-resistance conditions on the semiconductor material.

It will be understood that variations and modifications may be effected of the forms of the invention described above without departing from the spirit and scope of the novel concepts of this invention.

lclaim:

1. An electrically operated display screen for displaying a lighted pattern at a front side thereof and for receiving energy from a side thereof to form or change the display pattern, said display screen comprising: a first layer of conductive material; first and second active layers in electrical connection along their confronting surface areas, one of said first and second active layers being disposed on said first layer of conductive material, said one of said first and second active layers being an electroluminescent material having means to emit light of at least a given amount ofintensity at selected portions thereof as a result of a given exciting current and voltage across said selected portions thereof, and the other of said first and second active layers being a variable resistance memory semiconductor material including means capable of having discrete portions thereof selectively reversibly stably structurally changed in configuration or conformation by only momentary application of said energy thereto, selectively to one stable condition of high resistance or a different stable structural condition of low resistance, said different conditions of high and low resistance persisting indefinitely after all sources of energy have been removed therefrom, a second layer of conductive material disposed on one of said first and second active layers in electrical connection along the confronting surface areas thereof at the side remote from said first layer of conductive material, the layer of conductive material nearest said layer of variable resistance memory material being transparent to said energy which alters the same between said highand low-resistance conditions, the one of said first and second layers of conductive material on the viewing side of the display screen being transparent to light emitted by the layer of electroluminescent material, and said first and second layers of conductive'material forming electrodes for connection to a voltage source such that said exciting current and voltage are present between said first and second layers of conductive material only in the regions of said selected discrete portions where said variable resistance memory material is in said condition of low resistance to energize said selected portion of said electroluminescent material to provide a light-emitting display pattern on the viewing side ofthe display screen.

2. The electrically operated display screen according to claim 1 wherein said layer of conductive material nearest said layer of variable resistance memory material is transparent to a narrow beam of energy capable of altering discrete portions of said layer of variable resistance memory material from said low-resistance to said high-resistance conditions and also transparent to a wide beam of energy capable of altering simultaneously all the portions of said variable resistance memory material from said low resistance to said high-resistance structural condition.

3. The electrically operated display screen according to claim 1 wherein the voltage source to be connected to said first and second layers of conductive material is an alternating current voltage source and said first and second active layers are selected to have relative capacitive reactances wherein the impedance of discrete portion of said electroluminescent material is substantially greater than the impedance of the corresponding discrete portion of said variable resistance memory semiconductor material when in the high-resistance condition and in such condition the impedance of said variable resistance memory semiconductor material being sufficient to reduce the voltage across said electroluminescent material below the significant light-emitting value thereof.

4. The electrically operated display screen according to claim 1 wherein said layer of conductive material nearest said layer of variable resistance memory material is at the rear of the screen and the layer of conductive material in the viewing side of the screen is the other layer of conductive material.

5. The electrically operated display screen according to claim 4 in combination with means mounted behind said layer of conductive material nearest said layer of variable resistance memory material for altering discrete selected portions of the same between said highand low-resistance conditions thereof.

6. The electrically operated display screen according to claim 1 wherein said first and second layers of conductive material and said first and second active layers are deposited on a substrate.

7. The electrically operated display screen according to claim 6 wherein said substrate is adjacent said layer of conductive material nearest said layer of variable resistance memory material and together therewith form the rear portion of said display screen, said substrate and the last-mentioned layer of conductive material are transparent to said energy capable of altering discrete portions of said layer of variable resistance memory material between said highand low-resistance conditions.

8. The electrically operated display screen according to claim 1 in combination with a closure for receiving said display screen; a first energy source in said closure for directing a narrow beam of energy toward said layer of conductive material nearest said layer of variable resistance memory material to alter the resistance condition of said variable resistance memory material between said highand low-resistance conditions; deflection means in said closure for deflecting said narrow beam of energy to a desired point on the display screen; a second energy source in said closure for directing a wide beam of energy toward the rear of the display screen to reset the portions of said variable resistance memory material from said low-resistance condition back to said highresistance condition; and control means mounted outside of the closure and connected to said first and second energy sources and said deflection means to control the operation thereoffor changing the display pattern on the display screen.

9. The electrically operated display screen according to claim 8 forms an exterior wall of said closure from which display patterns can be viewed.

10. The electrically operated display screen according to claim 3 wherein said layer of electroluminescent material has a nonlinear voltage-brightness characteristic to provide a region where relatively small changes of voltage produce relatively large changes of brightness in said electroluminescent material 11. The display screen according to claim 1 in combination with: a source of exciting current and voltage for said electroluminescent material which source is coupled across said layers of conductive material to provide said given exciting current and voltage at those points of said electroluminescent material which are adjacent said discrete portions of said variable resistance memory material in said stable low-resistance condition, the portions of said electroluminescent material adjacent discrete portions of said variable resistance memory material in said high-resistance condition being devoid of said exciting current and voltage, and energy source means for selectively altering any of said discrete portions of said variable resistance memory material through said energy transparent layer of conductive material nearest said layer of variable resistance memory material from said high-resistance to said low-resistance condition or from said low-resistance to said high-resistance condition in the absence of any other source of current or voltage.

12. In combination: a display screen for displaying a lighted pattern, said display screen including light-emitting material distributed over various portions of the display screen, each of the various portions of said light-emitting material distributed over said Screen being capable of emitting light of at least a given minimum amount of intensity when sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled in series with said respective portions of said light-emitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereof is relatively high and a different structural condition where the resistance thereof is relatively low, the impedance of each portion of light-emitting material being appreciably larger than that of the high-resistance condition of the associated portion of said variable resistance memory material, so the voltage changes across each portion of the light-emitting material is relatively small as the associated portion of the variable resistance memory material varies between said relatively highand low-resistance conditions, said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different structural conditions of high and low resistance persisting indefinitely after all sources of energy has been removed therefrom, a source of exciting voltage coupled across said series connected portions of said light-emitting and variable resistance memory materials, each of said portions of said light-emitting material receiving said sufficient exciting voltage from said voltage source when such portion of light emitting material is connected in series with a portion of said variable resistance memory material in said condition of low resistance and receiving insufficient exciting voltage when said associated portion of variable resistance memory material is in said condition of low resistance, said respective portions of light-emitting material having a nonlinear brightness-voltage characteristic wherein with the application of two similar relatively high levels of voltage thereto the amount of light generated varies from a point where little or no light emission occurs to a point of substantial light emission, the relative values of the impedances of said series connected portions of said light-emitting material and variable resistance memory materials being such that the voltage applied to any of said portions of light-emitting material as the associated portion of variable resistance memory material is structurally changed to said conditions of high and low resistance varies between said two similar relatively high levels; and a source of energy to be applied to said portions of variable resistance memory material selectively structurally to change the same selectively to said condition of high resistance or to said condition of low resistance.

13. The combination ofclaim 12 wherein said means ofsaid portions of variable resistance memory material are capable of being altered by application of said energy thereto to different relative conditions of low resistance, so appreciably varying light intensities can be produced by said various portions of light-emitting material.

14. In combination: a display screen for displaying a lighted pattern at a front side thereof, said display screen including light-emitting material distributed over various portions of said display screen, each of the various portions of said lightemitting material distributed over said screen being capable of emitting light of at least a given minimum amount of intensity when sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled with said respective portions of said light-emitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereofis relatively high and a different structural condition where the resistance thereofis relatively low. said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different structural condition of high and low resistance persisting indefinitely after all sources of energy has been removed therefrom; a source of exciting voltage coupled to said portions of said light-emitting material; each of said portions of said light-emitting material being related to the associated portion of variable resistance memory material to receive said sufficient exciting voltage from said voltage source when said associated portion of variable resistance memory material is in said stable condition of low resistance and not to receive said sufficient exciting voltage when said associated portion of variable resistance memory material is in said stable condition of low resistance, and said portions of said variable resistance memory material being capable of being altered by application of said energy thereto to different relative states of low resistance, so appreciably varying light intensities can be produced by said various portions of lightemitting material; and a source of energy for selective application to said portions of variable resistance memory material to alter the same selectively to said various conditions of high and low resistance.

15. The combination of claim 14 wherein said portions of variable resistance memory material are positioned to receive said energy directed upon one side thereof in varying degrees at different positions.

16. A display screen for displaying a lighted pattern, said display screen including light-emitting material distributed over various portions ofthe display screen, each ofthe various portions of said light-emitting material distributed over said screen being capable of emitting light of at least a given minimum amount of intensity when a sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled with said respective portions of said lightemitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereof is relatively high and a different structural condition where the resistance thereof is relatively low, said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different stable conditions of high and low resistance persisting indefinitely after all sources of energy have been removed therefrom, means for applying a voltage source to said portions of said light-emitting material, each of said portions of light-emitting material being related to the associated portion of variable resistance memory material to receive said sufficient exciting voltage from said voltage source when said associated portion of variable resistance memory material is in one of said stable conditions and not to receive said sufficient exciting voltage when said associated portion of variable resistance memory material is in the other stable condition, and said portions of variable resistance memory material being adapted to receive a source of energy selectively structurally to change the same to said stable condition of high resistance or to said stable condition oflow resistance.

17. The display screen of claim 16 wherein said portions of light-emitting material distributed over said screen are form ed as a single integral layer of material, and said portions of variable resistance memory material forming a single integral layer, and the layer of variable resistance memory material being exposed to a source of energy to be applied from one side thereof.

18. The display screen of claim 16 wherein each of said portions of light-emitting material is connected in series circuit relation with said associated portion of variable resistance memory material, and each said associated portion of variable resistance memory material being in its low-resistance condition to provide said sufficient exciting voltage to the associated portion ofliglit-emitting material.

. UNITED STATES PATENT OFFICE QERTWICATE 0F CGRREQTWN 3,64%741 Dated February 22, 1972 Stanford R. Ovshinsky Patent No.

Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below: I

column 2, 11 15, last formula "801530818 should read G'e1 Se S2 column 11, line 11, low" should read high column 12, line 2-, "low" should read high Signed and sealed this zth dayof December 1972.

(SEAL) Atteac:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents U.S GOVERNMENT PRINTING OFFICE 1969 O-356334,

FORM P c-1050 (10-69) 

1. An electrically operated display screen for displaying a lighted pattern at a front side thereof and for receiving energy from a side thereof to form or change the display pattern, said display screen comprising: a first layer of conductive material; first and second active layers in electrical connection along their confronting surface areas, one of said first and second active layers being disposed on said first layer of conductive material, said one of said first and second active layers being an electroluminescEnt material having means to emit light of at least a given amount of intensity at selected portions thereof as a result of a given exciting current and voltage across said selected portions thereof, and the other of said first and second active layers being a variable resistance memory semiconductor material including means capable of having discrete portions thereof selectively reversibly stably structurally changed in configuration or conformation by only momentary application of said energy thereto, selectively to one stable condition of high resistance or a different stable structural condition of low resistance, said different conditions of high and low resistance persisting indefinitely after all sources of energy have been removed therefrom, a second layer of conductive material disposed on one of said first and second active layers in electrical connection along the confronting surface areas thereof at the side remote from said first layer of conductive material, the layer of conductive material nearest said layer of variable resistance memory material being transparent to said energy which alters the same between said high- and low-resistance conditions, the one of said first and second layers of conductive material on the viewing side of the display screen being transparent to light emitted by the layer of electroluminescent material, and said first and second layers of conductive material forming electrodes for connection to a voltage source such that said exciting current and voltage are present between said first and second layers of conductive material only in the regions of said selected discrete portions where said variable resistance memory material is in said condition of low resistance to energize said selected portion of said electroluminescent material to provide a light-emitting display pattern on the viewing side of the display screen.
 2. The electrically operated display screen according to claim 1 wherein said layer of conductive material nearest said layer of variable resistance memory material is transparent to a narrow beam of energy capable of altering discrete portions of said layer of variable resistance memory material from said low-resistance to said high-resistance conditions and also transparent to a wide beam of energy capable of altering simultaneously all the portions of said variable resistance memory material from said low resistance to said high-resistance structural condition.
 3. The electrically operated display screen according to claim 1 wherein the voltage source to be connected to said first and second layers of conductive material is an alternating current voltage source and said first and second active layers are selected to have relative capacitive reactances wherein the impedance of discrete portion of said electroluminescent material is substantially greater than the impedance of the corresponding discrete portion of said variable resistance memory semiconductor material when in the high-resistance condition and in such condition the impedance of said variable resistance memory semiconductor material being sufficient to reduce the voltage across said electroluminescent material below the significant light-emitting value thereof.
 4. The electrically operated display screen according to claim 1 wherein said layer of conductive material nearest said layer of variable resistance memory material is at the rear of the screen and the layer of conductive material in the viewing side of the screen is the other layer of conductive material.
 5. The electrically operated display screen according to claim 4 in combination with means mounted behind said layer of conductive material nearest said layer of variable resistance memory material for altering discrete selected portions of the same between said high- and low-resistance conditions thereof.
 6. The electrically operated display screen according to claim 1 wherein said first and second layers of conductive material and said first and second active layers are dePosited on a substrate.
 7. The electrically operated display screen according to claim 6 wherein said substrate is adjacent said layer of conductive material nearest said layer of variable resistance memory material and together therewith form the rear portion of said display screen, said substrate and the last-mentioned layer of conductive material are transparent to said energy capable of altering discrete portions of said layer of variable resistance memory material between said high- and low-resistance conditions.
 8. The electrically operated display screen according to claim 1 in combination with a closure for receiving said display screen; a first energy source in said closure for directing a narrow beam of energy toward said layer of conductive material nearest said layer of variable resistance memory material to alter the resistance condition of said variable resistance memory material between said high- and low-resistance conditions; deflection means in said closure for deflecting said narrow beam of energy to a desired point on the display screen; a second energy source in said closure for directing a wide beam of energy toward the rear of the display screen to reset the portions of said variable resistance memory material from said low-resistance condition back to said high-resistance condition; and control means mounted outside of the closure and connected to said first and second energy sources and said deflection means to control the operation thereof for changing the display pattern on the display screen.
 9. The electrically operated display screen according to claim 8 forms an exterior wall of said closure from which display patterns can be viewed.
 10. The electrically operated display screen according to claim 3 wherein said layer of electroluminescent material has a nonlinear voltage-brightness characteristic to provide a region where relatively small changes of voltage produce relatively large changes of brightness in said electroluminescent material
 11. The display screen according to claim 1 in combination with: a source of exciting current and voltage for said electroluminescent material which source is coupled across said layers of conductive material to provide said given exciting current and voltage at those points of said electroluminescent material which are adjacent said discrete portions of said variable resistance memory material in said stable low-resistance condition, the portions of said electroluminescent material adjacent discrete portions of said variable resistance memory material in said high-resistance condition being devoid of said exciting current and voltage, and energy source means for selectively altering any of said discrete portions of said variable resistance memory material through said energy transparent layer of conductive material nearest said layer of variable resistance memory material from said high-resistance to said low-resistance condition or from said low-resistance to said high-resistance condition in the absence of any other source of current or voltage.
 12. In combination: a display screen for displaying a lighted pattern, said display screen including light-emitting material distributed over various portions of the display screen, each of the various portions of said light-emitting material distributed over said screen being capable of emitting light of at least a given minimum amount of intensity when sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled in series with said respective portions of said light-emitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereof is relatively high and a different structural condition where the resistance thereof is relatively low, the impedance of each portion of light-emitting material being appreciably larger than that oF the high-resistance condition of the associated portion of said variable resistance memory material, so the voltage changes across each portion of the light-emitting material is relatively small as the associated portion of the variable resistance memory material varies between said relatively high- and low-resistance conditions, said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different structural conditions of high and low resistance persisting indefinitely after all sources of energy has been removed therefrom, a source of exciting voltage coupled across said series connected portions of said light-emitting and variable resistance memory materials, each of said portions of said light-emitting material receiving said sufficient exciting voltage from said voltage source when such portion of light-emitting material is connected in series with a portion of said variable resistance memory material in said condition of low resistance and receiving insufficient exciting voltage when said associated portion of variable resistance memory material is in said condition of low resistance, said respective portions of light-emitting material having a nonlinear brightness-voltage characteristic wherein with the application of two similar relatively high levels of voltage thereto the amount of light generated varies from a point where little or no light emission occurs to a point of substantial light emission, the relative values of the impedances of said series connected portions of said light-emitting material and variable resistance memory materials being such that the voltage applied to any of said portions of light-emitting material as the associated portion of variable resistance memory material is structurally changed to said conditions of high and low resistance varies between said two similar relatively high levels; and a source of energy to be applied to said portions of variable resistance memory material selectively structurally to change the same selectively to said condition of high resistance or to said condition of low resistance.
 13. The combination of claim 12 wherein said means of said portions of variable resistance memory material are capable of being altered by application of said energy thereto to different relative conditions of low resistance, so appreciably varying light intensities can be produced by said various portions of light-emitting material.
 14. In combination: a display screen for displaying a lighted pattern at a front side thereof, said display screen including light-emitting material distributed over various portions of said display screen, each of the various portions of said light-emitting material distributed over said screen being capable of emitting light of at least a given minimum amount of intensity when sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled with said respective portions of said light-emitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereof is relatively high and a different structural condition where the resistance thereof is relatively low, said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different structural condition of high and low resistance persisting indefinitely after all sources of energy has been removed therefrom; a source of exciting voltage cOupled to said portions of said light-emitting material; each of said portions of said light-emitting material being related to the associated portion of variable resistance memory material to receive said sufficient exciting voltage from said voltage source when said associated portion of variable resistance memory material is in said stable condition of low resistance and not to receive said sufficient exciting voltage when said associated portion of variable resistance memory material is in said stable condition of low resistance, and said portions of said variable resistance memory material being capable of being altered by application of said energy thereto to different relative states of low resistance, so appreciably varying light intensities can be produced by said various portions of light-emitting material; and a source of energy for selective application to said portions of variable resistance memory material to alter the same selectively to said various conditions of high and low resistance.
 15. The combination of claim 14 wherein said portions of variable resistance memory material are positioned to receive said energy directed upon one side thereof in varying degrees at different positions.
 16. A display screen for displaying a lighted pattern, said display screen including light-emitting material distributed over various portions of the display screen, each of the various portions of said light-emitting material distributed over said screen being capable of emitting light of at least a given minimum amount of intensity when a sufficient exciting voltage is applied to the same, variable resistance memory material distributed over said screen and having portions thereof electrically coupled with said respective portions of said light-emitting material, said variable resistance memory material having at least two stable conditions respectively where the material has one structural condition where the resistance thereof is relatively high and a different structural condition where the resistance thereof is relatively low, said portions of variable resistance memory material including means capable of being reversibly stably structurally changed in configuration or conformation, by only momentary application of energy thereto, selectively to said stable condition of high resistance or to said stable condition of low resistance, said different stable conditions of high and low resistance persisting indefinitely after all sources of energy have been removed therefrom, means for applying a voltage source to said portions of said light-emitting material, each of said portions of light-emitting material being related to the associated portion of variable resistance memory material to receive said sufficient exciting voltage from said voltage source when said associated portion of variable resistance memory material is in one of said stable conditions and not to receive said sufficient exciting voltage when said associated portion of variable resistance memory material is in the other stable condition, and said portions of variable resistance memory material being adapted to receive a source of energy selectively structurally to change the same to said stable condition of high resistance or to said stable condition of low resistance.
 17. The display screen of claim 16 wherein said portions of light-emitting material distributed over said screen are formed as a single integral layer of material, and said portions of variable resistance memory material forming a single integral layer, and the layer of variable resistance memory material being exposed to a source of energy to be applied from one side thereof.
 18. The display screen of claim 16 wherein each of said portions of light-emitting material is connected in series circuit relation with said associated portion of variable resistance memory material, and each said associated portion of variable resistance memory material being in its low-resistance condition to provide said sufficient exciting voltage to the assoCiated portion of light-emitting material. 